<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button id="b1">按钮1</button>
    <button id="b2">按钮2</button>
    <button onclick="demo()">按钮3</button>
    <script type="text/javascript">
        const btn1 = document.getElementById("b1")
        btn1.addEventListener("click",()=>{
            alert("按钮1被点击了")
        })
        const btn2 = document.getElementById("b2")
        btn2.onclick=()=>{
            alert("按钮2被点击了")
        }
       function demo(){
           alert("按钮3被点击了")
       }
    </script>
</body>
</html>